Liquidus and solidus

While chemically pure materials have a single melting point, chemical mixtures often partially melt at the solidus temperature (T_S or T_sol), and fully melt at the higher liquidus temperature (T_L or T_liq). The solidus is always less than or equal to the liquidus, but they need not coincide. If a gap exists between the solidus and liquidus it is called the freezing range, and within that gap, the substance consists of a mixture of solid and liquid phases (like a slurry). Such is the case, for example, with the olivine (forsterite-fayalite) system, which is common in Earth's mantle.^[1]